This invention relates to a process for the preparation of 1,1'-bi-2-naphthols.
1,1'-Bi-2-naphthols are useful in the preparation of polyesters and polycarbonates.
Rutledge, U.S. Pat. No. 4,097,461, discloses a process for the coupling of alkylphenols, or 1-naphthols. The coupling products of 1-naphthols are 2,2'-binaphthols and 2,2'-dinaphthenoquinone.
Kulawski et al., Polish Pat. No. 87,440 (Chem. Abs. 90:151874x (1979)), disclose a process for the coupling of naphthols by oxidation in the presence of a stoichiometric amount of an aqueous solution of FeCl.sub.3. The products are identified as 4,4'-dihydroxy-1,1'-binaphthol and 1,1'-dihydroxy-2,2'-dinaphthol.
The known processes for the oxidative coupling of naphthols have disadvantages. The formation of dinaphthenoquinones in large amounts as a by-product is a significant disadvantage. The use of stoichiometric amounts of iron ions to promote the oxidation of the naphthols is a further disadvantage. Such large amounts of metal are very costly. Purification of the product is extremely difficult and costly when such large amounts of iron ions are used.
What is needed is a process for the coupling of 2-naphthols to prepare 1,1'-bi-2-naphthols wherein dinaphthenoquinones are not co-produced in significant amounts. What is further needed is a process wherein the metal ions are used in catalytic amounts as opposed to stoichiometric amounts, resulting in a less costly process wherein the purification of the products is simplified.